Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$238.74	5.112%	$250.9444	$250.94	$250.95	$250.90
Purchase #2	$152.68	12.507%	$171.7757	$171.78	$171.80	$171.80
Purchase #3	$99.61	5.431%	$105.0198	$105.02	$105.00	$105.00
Purchase #4	$159.80	6.625%	$170.3868	$170.39	$170.40	$170.40
Purchase #5	$143.91	11.716%	$160.7705	$160.77	$160.75	$160.80
Purchase #6	$141.89	6.234%	$150.7354	$150.74	$150.75	$150.70
Purchase #7	$235.25	9.199%	$256.8906	$256.89	$256.90	$256.90
7 purchase totals =	$1,171.88		$1,266.5232	$1,266.53	$1,266.55	$1,266.50